Effects of short photoperiod on the ability of golden hamster pituitaries to secrete prolactin and gonadotropins in vitro.

Transfer of male golden (Syrian) hamsters from a 14L:10D (light:dark) to a 5L:19D photoperiod induced significant changes in pituitary function tested in vitro. Within 27 days after transfer to a 5L:19D photoperiod, basal prolactin (Prl) release was significantly depressed and response to dopamine (DA) was significantly enhanced as compared to Prl release by pituitaries from 14L: 10D hamsters. Follicle-stimulating hormone (FSH) release tended to be depressed after 9 or 27 days of 5L:19D exposure, but the effect was not significant. After 77 days of 5L:19D exposure, Prl release was further suppressed, while FSH release surpassed that seen in 14L:10D pituitaries. In vitro FSH response to luteinizing hormone releasing hormone (LHRH) was also enhanced at this time. After 15 weeks of exposure to a short photoperiod, FSH secretion was still elevated above control levels, but Prl release and Prl response to DA were no longer different from that of 14L: 10D controls. Secretion of luteinizing hormone (LH) in vitro, either basal or LHRH stimulated, was not affected by photoperiod at any time tested. From these results, we conclude that short photoperiod exposure does not reduce the pituitary's ability to secrete LH or FSH, although secretion of Prl is severely attenuated.